PORTLAND, Ore. — Democratic presidential nominee Michael S. Dukakis on Friday rehired his longtime confidant John Sasso, who resigned under fire as campaign manager last year after distributing a videotape that helped sink the presidential candidacy of Delaware Sen. Joseph R. Biden Jr.

Dukakis made the announcement at a San Jose press conference before flying here to deliver an energetic attack on Vice President George Bush and his running mate, Sen. Dan Quayle. Dukakis said Sasso "made a very serious mistake," but "there was nothing illegal about what John did."

"A year is a long time," Dukakis said, suggesting that Sasso had been punished enough.

In Boston, Sasso appeared with campaign manager Susan Estrich and received a thunderous ovation from Dukakis campaign staffers and state government loyalists.

"What I did back in September was an error in judgment and I am sorry that it hurt Sen. Biden and his family," Sasso said.

Sasso resigned after he was unmasked as the source of an "attack video" which showed that Biden, a Dukakis rival for the nomination, had plagiarized a speech from British Labor Party leader Neil Kinnock. Before the revelation, Dukakis had denied that his campaign had anything to do with the tape.

For most of the last year, Dukakis kept his distance from his longtime aide, whom many observers had called Dukakis' political alter ego. Since July, however, Sasso has eased steadily closer to retaking an active role, speaking frequently with Dukakis and consulting with members of his staff.

His return as vice chairman of the campaign will give Dukakis a seasoned political tactician at his side, something many Democratic leaders have said his campaign has badly lacked. He will travel extensively with Dukakis while Estrich will remain as the day-to-day manager of the campaign staff.

"There are contrasts and weaknesses that are issues in this campaign," said Sasso, who will take a leave of absence from his job with an advertising firm. "I will not shy away from pointing those contrasts out."

Dukakis said Friday that he had talked with Biden--although not until Friday morning, after the decision had been made to rehire Sasso and word had begun to leak out. Biden "couldn't have been more gracious" about the decision, he said.

With Dukakis clearly happy about the return of the aide who has been the architect of his political career, his appearances Friday were more energetic and forceful than he has been in weeks.

"This week may represent some kind of a turning point in this campaign," Dukakis told the news conference in San Jose. "I'm feeling particularly good."

"We're going to be discussing Mr. Bush's record and my record, the record of the Republican Party and the Democratic Party's record. If (the campaign battle) is joined there, we'll win," he said.

Repeats Attacks

Later, speaking in Portland before a flag-waving, cheering crowd of thousands gathered in a downtown park, Dukakis repeated his attacks on Bush's record on education and ridiculed his proposal to put Quayle in charge of the nation's anti-drug efforts.

"Is there anyone here, is there any citizen in the United States of America who thinks that Dan Quayle is qualified to be the nation's drug czar?" Dukakis asked, drawing cheers, jeers and shouts of "He's a draft dodger" from the crowd.

The speech was the second time this week, and the first time ever in a public speech, that Dukakis has directly attacked Quayle. Wednesday in an interview with The Times, Dukakis, citing Quayle's voting record, suggested that Bush's running mate was unqualified to be President.

Dukakis elicited chants of "Where was George?" as he listed Reagan Administration education budget cuts, repeating charges he had made Thursday in Oakland.

Broad Smiles

The energetic speech, together with Sasso's return, brought broad smiles to the Dukakis entourage.

After several weeks of drift, Dukakis and his campaign appear to have recovered their stride. In the West Coast campaign swing that ended Friday, he has hit hard against Bush and Quayle and honed a message of "economic patriotism" that adds nationalistic tones to Dukakis' longstanding appeal to voters' anxieties about the nation's future.

Sasso's hiring is the most significant of several additions designed to add strength to the Democratic team as it heads into the final weeks of the campaign. It does, however, raise one potential problem for Dukakis, appearing to undermine his campaign emphasis on high ethical standards.

'Serious Trouble'

Quayle, campaigning in Alabama, said it was "another sign that the Dukakis campaign is in serious trouble."

Bush, aboard a small boat in Delaware where he was helping empty crab traps, was hailed by reporters in a nearby boat who shouted questions about Sasso. He seemed distracted for an instant and a crab pinched his hand.